Technical Field of the Invention
This invention generally relates to the field of producing zinc chloride and zinc sulfate from brines. More particularly, the invention relates to methods for the selective removal and recovery of zinc from geothermal brines that include zinc, preferably without the simultaneous removal of other ions from the brines, for the production of zinc chloride and zinc sulfate.
Description of the Prior Art
Geothermal brines are of particular interest for a variety of reasons. First, geothermal brines provide a source of power due to the fact that hot geothermal pools are stored at high pressure underground, which when released to atmospheric pressure, can provide a flash-steam. The flash-stream can be used, for example, to run a power plant. Additionally, geothermal brines contain useful elements, which can be recovered and utilized for secondary processes. With some geothermal waters and brines, binary processes can be used to heat a second fluid to provide steam for the generation of electricity without the flashing of the geothermal brine.
It is known that geothermal brines can include various metal ions, particularly alkali and alkaline earth metals, as well as silica, iron, lead, silver, zinc and manganese, in varying concentrations, depending upon the source of the brine. Recovery of these metals is potentially important to the chemical, pharmaceutical and electronics industries. Typically, the economic recovery of desired metals from natural brines, which may vary widely in composition, depends not only on the specific concentration of the desired metal, but also upon the concentrations of interfering ions, particularly silica, calcium and magnesium, because the presence of the interfering ions will increase recovery costs as additional steps must be taken to remove the interfering ions before the desired metals are recovered.
One problem associated with geothermal brines when utilized for the production of electricity results from scaling and deposition of solids. Silica and other solids that are dissolved within the geothermal brine precipitate out during all stages of brine processing, particularly during the cooling of a geothermal brine, and may eventually result in fouling of the injection wells or processing equipment.
Although conventional processing of ores and brines currently employed can be used to recover a portion of the zinc present in geothermal brines, there still exists a need to develop economic methods that are selective for the removal and recovery of zinc from the brines at high yields and high purity.